High parathyroid hormone levels and hypercalcemia induce 1,25(OH)2D3 synthesis, stimulating the transcription of CYP27B1 and increasing 1,25(OH)2D3 activity, with consequent down-stream action of CYP27B1 and suppression of parathyroid hormone [46]. The gene discussed is CYP27B1; the disease is hypercalcemia disease.